Channel for an automobile fluid

ABSTRACT

A transport tube for transporting a motor vehicle fluid, in particular a coolant, which tube comprises:  
     an inner layer ( 1 ) made of vulcanized elastomer material;  
     an outer layer ( 2 ) made of thermoplastic material that withstands the coolant chemically and that is impermeable thereto; and  
     an intermediate bonding layer ( 3 ) made of a material that is compatible with the materials of the inner and outer layers.

[0001] The present invention relates to a tube or a duct fortransporting a motor vehicle fluid and in particular a coolant in aninternal combustion engine, for example.

BACKGROUND OF THE INVENTION

[0002] Currently known prior art comprises:

[0003] rubber (ethylene-propylene diene monomer or “EPDM”) tubes whichmay optionally be reinforced depending on the pressure levels and/or thetemperatures of the fluids which flow therein;

[0004] metal tubes that are lined with and associated with rubber (EPDM)ducts enabling the movements and the vibrations generated by the engineto be absorbed; the rubber tubes are used in particular for making theconnections to members such as the engine, the radiator, the expansiontank . . . . The drawback of those systems lies in the significant sizeof the pipework given the existence of the metal tubes, in therelatively high rigidity of the system, and in the problems of the metaltubes corroding despite the lining applied thereto;

[0005] single layer pipes made of rigid thermoplastic such as polyamide(in particular PA 66) filled with glass fiber; these pipes are veryrigid and consequently have the drawback of transmitting vibration, andof giving off noise as a result of the vibration and also as a result ofthe flow of fluid passing therealong;

[0006] thermoplastic pipes having various rigid and flexible segmentsfor absorbing vibration and movements generated by the engine; however,the flexible portions must be reinforced by a structure which limitsboth their radial expansion and their axial lengthening; the flexibleportions are either made integrally with the rigid portions, orindependently of said rigid portions and are assembled thereto bywelding. The drawback of that technique essentially lies in itscomplexity and in the large number of manufacturing operations; and

[0007] multilayer pipes made of synthetic material that is eitherentirely thermoplastic, or thermoplastic only in part, in which case thethermoplastic portion forms the inner layer of the pipe; the drawback ofsuch a pipe lies in it being difficult, if not impossible, to connect tocurrent rigid endpieces (e.g. a spigot), thus making it necessary to usean intermediate connection piece.

OBJECTS AND SUMMARY OF THE INVENTION

[0008] To mitigate the drawbacks of the prior art, the inventionproposes a tube structure for transporting a fluid flowing in motorvehicle engines, and in particular a coolant, which tube structure alsosatisfies particularly strict specifications, and does so under goodeconomic production conditions. It is necessary for this type of tube tobe manufactured in simple manner and therefore at low cost, for it tocontinue to have some rigidity enabling it, in particular, to retain theshapes imposed on it prior to its final assembly, for it to present veryhigh performance with regard to permeability, and in particular, muchhigher performance than that of the rubber ducts used until now, andfinally, for said multilayer structure to be capable of withstandingassembly forces of the force-fit type without the various layers makingit up separating under the effect of said forces.

[0009] Thus to this end, the invention provides a tube for transportinga motor vehicle fluid such as a coolant, which tube comprises:

[0010] an inner layer made of vulcanized elastomer material;

[0011] an outer layer made of thermoplastic material that withstands thecoolant chemically and that is impermeable thereto; and

[0012] an intermediate bonding layer made of a material that iscompatible with the materials of the inner and outer layers.

[0013] In addition to satisfying the above-mentioned specifications,such a structure enables tubes to be made that are adapted to themechanical performance that is required of them. Thus, the inner layermade of vulcanized elastomer material has a thickness that is adapted,for example, to the dimensions of the projection on the rigid endpiecesonto which the tube is to be force fitted. In addition, the thickness ofthe outer layer made of thermoplastic is chosen as a function of thestiffness desired for the tube, which stiffness is compatible with thelevels of movement and of vibration allowed when the tube is installedin the vehicle. The thickness of the intermediate layer itself lies inthe range {fraction (1/10)}^(th) to {fraction (3/10)}^(ths) of amillimeter, said layer not having any mechanical function, but merelythe function of interconnecting the two layers which surround it.

[0014] In an embodiment of the tube of the invention, the vulcanizedelastomer of the inner layer is chosen from the components EPDM(polyolefin elastomer), nitrile polyvinyl chloride (PVC), andchlorosulfonated polyethylene (CSM).

[0015] The outer layer is chosen from the polyamides such as PA6, PA66,PA12. The outer polyamide can advantageously be filled with glass fiber.

[0016] Finally, the intermediate bonding layer is a substance based onethylene, acrylic ester, and maleic anhydride.

[0017] In a second variant embodiment of the tube of the invention, theabove-mentioned base structure, namely an elastomer layer, athermoplastic layer, and a bonding layer, is covered by a vulcanizedelastomer layer connected to the thermoplastic layer of the polyamidetype via an intermediate bonding layer of the type described above.

[0018] The advantage of the coating lies mainly in the fact that thetube presents a flexible coating to the outside atmosphere, therebydamping noise and impacts and, by its vulcanized elastomer nature,possesses a structure that is cross-linked in three dimensions, therebyhaving the advantage of presenting quite good resistance to fire due tothe fact that said structure does not collapse on itself under theeffect of heat.

BRIEF DESCRIPTION OF THE DRAWING

[0019] Other characteristics and advantages of the invention will appearon reading the following description, given by way of example and withreference to the accompanying drawing, in which:

[0020]FIG. 1 is a diagrammatic cross-section view of a tube constitutinga first embodiment of the invention; and

[0021]FIG. 2 is a diagrammatic cross-section view of a second embodimentof a tube of the invention.

MORE DETAILED DESCRIPTION

[0022] In the embodiment shown in the figures, the tube of the inventionis designed to form part of the engine cooling circuit and it comprisesan inner layer 1 made of a vulcanized elastomer material of thicknessconstituting about 50% to 80% of the total thickness of the tube.Examples of materials that are suitable for making the inner layer areas follows: ethylene propylene rubbers (ethylene propylene monomers or“EPMs” and EPDMs), nitrile butadiene rubbers (NBRs), acrylic estercopolymers (ACMs), NBR/PVCs, hydrogenated nitrile butadiene rubbers(HNBRs), acrylic ester ethylene copolymers (AEMs), silicone rubbers(MVQs), fluoroelastomers (FPMs), methyl fluoro silicone rubbers (FMQs),isobutene-isoprene rubbers (IIRs), isoprene rubbers (IRs), styrenebutadiene rubbers (SBRs), epichlorhydrine co-ethylene oxides (EO-ECOs),chloroprene rubbers (CRs), chlorosulfonated polyethylenes (CSMs),chlorinated polyethylenes (CPEs) . . . . This layer made of elastomermaterial has two main functions, i.e. firstly to enable significantdeformation while maintaining tight contact with rigid endpieces of thenipple or spigot type when a tube of the invention is connected to amember provided with such an endpiece, and secondly to constitute adamper of the vibration to which the tube of the invention can besubject, which vibration can originate externally or internally, such aswater hammer or other sudden variations in the flow of liquidtransported by the tube.

[0023] The outer layer 2 of the tube of the invention is a polyamidelayer, said polyamide layer being made of polyamide 12, or preferablybeing made of polyamide 66 or polyamide 6, both of which may optionallybe filled with glass fiber depending on the mechanical performancedesired for the tube. A thermoplastic material could also be chosen thatmeets characteristics which satisfy “class C” compliance criteriarelating to all motor vehicle fluids in trials standardized by motorvehicle manufacturers. The thickness of the outer layer constitutesapproximately the remainder to 100% of the total thickness beyond thethickness of the inner layer. The difference existing between the totalthickness and the sum of said two thicknesses is reserved for theintermediate bonding layer 3 (of 1 to {fraction (3/10)}^(ths) of a mm),said intermediate layer being made of a material that is compatible withthe materials of both layers 1 and 2, and in particular being asubstance based on ethylene, acrylic ester, and maleic anhydride, and isavailable on the market under the tradename LOTADER, for example.

[0024] Such a substance is easy to fabricate since it can be coextrudedwith each of the layers.

[0025] In a variant embodiment shown in FIG. 2, the base structure ofFIG. 1 is covered by another layer 4 which is constituted by avulcanized elastomer material of the same type as that identified forlayer 1, said layer 4 being connected to layer 2 via a bonding layer 5of the same type as layer 3 described above. This type of flexiblecovering imparts several qualities to the tube made in this way.Firstly, it is agreeable to touch, which corresponds to a desire ofmotor vehicle manufactures. Secondly, the flexible layer constitutes ananti-noise element in that it damps the impacts and vibration to whichthe tube is subjected from the outside. Thirdly, a vulcanized elastomerstructure presents three-dimensional cross-linking which constitutes afactor in improving the ability of the pipe to resist fire, since saidstructure does not tend to collapse on itself under heat as a result ofsaid three-dimensional cross-linking.

[0026] Naturally, an advantage of the tube of the invention is that itcan be thermoformed by means of its layer 2 made of thermoformablethermoplastic. In addition, the inner layer made of elastomer materialconstitutes, for the thermoplastic at the moment of thermoforming, asort of support for the polyamide layer which prevents the tube fromkinking. Finally, it should be noted that the heat applied to theassembly at the moment of thermoforming contributes to vulcanizing theinner layer and/or the outer layer.

[0027] The pipe of the invention is suitable for many motor vehiclefluids (brake or power steering fluids, . . . ).

1/ A tube for transporting a motor vehicle fluid, in particular acoolant, the tube comprising: an inner layer (1) made of vulcanizedelastomer material; an outer layer (2) made of thermoplastic materialthat withstands the coolant chemically and that is impermeable thereto;and an intermediate bonding layer (3) made of a material that iscompatible with the materials of the inner and outer layers. 2/ Atransport tube according to claim 1, wherein the vulcanized elastomer ofthe inner layer is chosen from the components EPDM (polyolefinelastomer), nitrile polyvinyl chloride (PVC), and chlorosulfonatedpolyethylene (CSM). 3/ A tube according to claim 2, wherein the outerlayer is chosen from the polyamides PA6, PA66, PA12. 4/ A tube accordingto claim 3, wherein the outer polyamide is filled with glass fiber. 5/ Atube according to claim 1, wherein the bonding layer is a substancebased on ethylene, acrylic ester, and maleic anhydride. 6/ A tubeaccording to claim 1, including a coating layer (4) made of vulcanizedelastomer material covering the layer (2) made of thermoplasticmaterial, and bonded to said layer (2) via an intermediate bonding layer(5) made of a material that is compatible with the coating layer (4) andthe layer (2) made of thermoplastic material.